Support verification of Notary Project signatures created with Azure Key Vault in Ratify

[yizha1]

This issue is to ask the support of verifying signatures during image deployment to ensure only trusted images are deployed on Azure Kubernetes Service (AKS) clusters. The signatures are produced with Azure Key Vault (AKV) according to the following guideline:

Sign container images with Notation and Azure Key Vault using a CA-issued certificate
Sign container images with Notation and Azure Key Vault using a self-signed certificate

In AKS clusters, Ratify will work with Azure policy to deny/audit images that fali policy validation.